Explain SMBC — the wiki for Saturday Morning Breakfast Cereal

This comic plays on the classic pop culture trope of "three kids stacked in a trenchcoat" pretending to be an adult -- most famously associated with Vincent Adultman from the TV show BoJack Horseman. In the comic, a man wearing a trenchcoat, hat, and sunglasses approaches a movie theater ticket counter and nervously asks for a ticket to "Sticky Heat," an R-rated film, slipping between "we" and "I" as he speaks. The ticket seller addresses him as "Mr. Adultstein" and sells him the ticket without issue, while privately thinking "Poor guy."

The punchline is delivered in the caption at the bottom: "Sufferers from Adolescent Triad Delusion believe themselves to be three children in a trenchcoat." The joke inverts the original trope entirely. Instead of three kids pretending to be one adult, this is one adult who has a psychological delusion that he is actually three children stacked up. The humor comes from the reversal -- the ticket seller's sympathy suggests this is a known, pitiable condition rather than a deception. The name "Adultstein" is itself a joke, echoing the absurd naming conventions of the original trope (like "Vincent Adultman") and suggesting the man has constructed an identity around his delusion of being children pretending to be an adult. The comic finds humor in medicalizing an absurd fictional trope and treating it with deadpan sympathy.